Axial flow turbomachines, such as a gas turbine engine, include rotors having a plurality of individual blades distributed about the periphery for interacting with an annularly flowing stream of working fluid. It is well known to provide seals along the axially-running gap formed between adjacent blade platforms in such rotor assemblies to prevent the occurrence of radially inward flow of such working fluid. Such interblade seals may be disposed between the rotor disk rim and the underside of the blade platforms within a cavity formed between adjacent blades. This cavity, termed the "damper cavity" is typically adapted to receive an inertial vibration damper for reducing unwanted rotor rim vibration. Such seals may be formed of thin sheet metal as disclosed in U.S. Pat. No. 4,505,642 by Hill, or other flexible construction as in U.S. Pat. No. 4,183,720 by Brantley.
A combination seal and vibration damper is shown in U.S. Pat. No. 4,101,245 by Hess et al. U.S. Pat. No. 4,457,668 by Hallinger shows a trough-shaped damper which channels a radially outward flowing stream of cooling air into an axial passage for cooling engine structure adjacent the opposite face of the rotor assembly.
Seals thus known in the prior art are well suited for preventing radial inflow of the working fluid past the blade platforms and into the damper cavity. Since the typical working fluid in a turbine section of a gas turbine engine consists of pressurized, high temperature combustion products, and since the damper cavity adjoins that portion of the rotating turbine disk which is under the highest material stress, the benefits of such sealing are also well known and continue to inspire designers to seek more effective, inexpensive, and easier to assemble sealing arrangements.
In addition to a radial pressure differential across the blade platform which attempts to induce the working fluid to flow radially between adjacent turbine blades toward the center line of the turbomachine, there is also typically an axial pressure gradient resulting from the successive compression or expansion of the annularly flowing working fluid. This axial pressure gradient also attempts to force working fluid into the damper cavity at the higher pressure face of the rotor assembly, bypassing the rotor blades and, for a turbine rotor assembly in a gas turbine engine, potentially overheating and inducing premature degradation of the turbine disk rim.
Interblade seals of the prior art, designed primarily to seal against radial flow of the working fluid, are not well adapted for preventing axial flow thereof. For example, the combined damper and seal of Hess et al extends between front and rear annular rotor disk sideplates which provide the desirable axial barrier against flow into the damper cavity. The combined structure of the Hess seal-damper is structurally stronger and heavier than the sheet metal and ribbon seals of Hill and Brantley, respectively, thus achieving good axial sealing force against the sideplates at the expense of reduced conformability of the combined member against the underside of the blade platforms.
Conversely, the thin and flexible seals of Hill and Brantley are easily conformed by the centrifugal acceleration induced by the rotation of the rotor assembly, but do not provide sufficient axial rigidity to engage the rotor sideplates to provide an effective, positive axial seal. The Hallinger seal-damper, rather than attempting to thwart axial gas flow, is configured to assist and direct axially flowing cooling air through the corresponding damper cavity.
What is needed is a sealing means which combines both axial and radial sealing ability in a lightweight, conformable seal member.